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Local anesthetic agents, benzocaine and butamben were compared for their permeabilities to silicone membrane and stabilities against hydrolytic degradations in 0.05N NaOH solutions. Butamben permeated through the membrane from the suspension to the same extent as benzocaine in spite of smaller solubility in water. Calculated stability of butamben in suspension was about 10 times greater than benzocaine due to smaller hydrolytic rate constant and smaller solubility. These properties of butamben may be favorable for the delivery system using a silicone membrane as a release-controlling barrier.